A cell line was derived from a metastatic, human melanoma. It is producing peptides that can stimulate an untransformed cell line to reversibly express a transformed phenotype. This transformed phenotype is expressed in monolayer as a disorganized growth pattern and in an anchorage-independent growth (AIG) assay as colonies forming in soft-agar from single seeded cells. One of the peptides in this mixture contributing to this activity is an epidermal growth factor-like growth factor that has a molecular weight of approximately 26,000 daltons as determined by gel permeation chromatography on Bio-Gel P-30 in 1 M acetic acid. This appears to be present at concentrations between 210 and 1,000 nanograms/ml. This EGF-like activity requires a second peptide to efficiently stimulate AIG. The second required peptide in this mixture has a modulator activity in that it appears to require the presence of either EGF or an EGF-like activity to efficiently stimulate large colony formation. This TGF-beta activity has an apparent molecular weight of approximately 21,000 daltons. Both of these peptides have physical properties that are distinctly different from those previously reported for the TGFs. These "ectopic" peptides may play a role in the expression of the transformed phenotype of the tumor cells producing them. Molecular clones have been derived to determine which genes are regulated by these growth and modulating factors. This knowledge will increase our understanding of the role these factors play in the expression of the transformed state.